London’s water treatment plants are tasked with purifying the water, but major storms reportedly “overwhelm” the operations and allow some sewage water to make its way into the river.

James Robson, a senior curator at Sea Life London, told The Independent that the addictive drug can have a similar impact on marine animals as it does on humans.

“Drugs which affect us will almost always affect all animal life, and invertebrates a little bit more because their biochemistry is much more sensitive,” Mr Robson said.

“Essentially everything in the water will be affected by drugs like these. A lot of the triggers and the ways that cocaine affects the system is really primal.”

The cocaine problem plaguing eels has been discussed before.

Researchers from the University of Naples Federico II studied the effects of cocaine on eels back in June 2018, publishing the results in the peer-reviewed journal Science Of The Total Environment.

“Data shows a great presence of illicit drugs and their metabolites in surface waters worldwide,” biologist Anna Capaldo, lead author of the 2018 study, told National Geographic at the time.

The group of biologists put eels in water with drug residue and discovered that it made them hyperactive and drastically changed their bodies.

“All the main functions of these animals could be altered,” Dr Capaldo said.

She explained that the changes occur in the eels’ muscles, hormones and brain after cocaine exposure.

Eels in the Thames aren’t as closely exposed to the drug as those in the 2018 study — so it doesn’t necessarily mean they’re getting “high” from the run-off.

“You haven’t got a lot of disco-dancing fish down the bottom of the Thames,” Mr Robson joked to The Independent.

It does, however, spark a debate about waste water treatment in the city.

“You can basically treat anything to any degree of purity, it’s just about how much money you want to put into the treatment process,” Daniel Snow, director of the Water Sciences Laboratory at the University of Nebraska, told National Geographic.